This invention relates to packaged electronic devices in general and more particularly to electronic devices having peripheral carrier structures.
The packaging technology for electronic components has many challenges facing it. Electronic components, such as integrated circuits (ICs), are becoming very dense with ultra large and very large scale integration (ULSI and VLSI). One challenge brought to packaging technology by such complex integration is manufacturing reliable packages with a high lead count. Leads are external to the package and are used to make electrical contacts to the semiconductor die located within the package. Higher levels of integration require more electrical connections, thus more leads. However, at the same time both the manufacturers and users of semiconductor devices want the size of the die and package to be small in order to minimize the device footprint. The footprint is the space required to mount the device onto a substrate, typically a printed circuit (PC) board.
One way of conserving PC board space is to stack components on top of one another. While this reduces the footprint, the technique has not become an industry standard and must overcome problems such as heat dissipation and new, unproven assembly procedures. Another way is to simply shrink existing components and packages. This is a widely practiced method and from a packaging aspect can be accomplished by reducing the pitch of the leads, or the lead-to-lead distance. Leadframe manufacturers have been successful, to a degree, in producing fine-pitch leadframes. A technology known as TAB (tape automated bonding) has also been helpful in allowing semiconductor manufacturers to produce fine-pitch packages. But with these packages comes another problem, namely handling. In making fine-pitch leadframes, manufacturers reduce the thickness and width of each lead, making them more fragile. On a packaged semiconductor device, the fragile leads are very susceptible to damage, especially during subsequent handling operations, testing, and shipping.
Various ways of preventing or minimizing lead damage have been established. For example, automation has been implemented to reduce handling operations, sockets are designed to minimize damage during testing, and prior to shipment the devices are placed in specially designed rails or trays. Another way of protecting fragile leads which is gaining popularity and is becoming an industry standard is the use of a protective carrier structure. The carrier structure is formed around the device, spaced apart from the package body, and has exposed contact points which allow for testing before the leads become free-standing and are formed into their final shape. Hence, leads are protected from damage during many handling operations and testing. Devices can be excised from the carrier just prior to shipment or can be shipped within the carrier, reducing the susceptibility to lead damage even further.
A draw-back to using a carrier structure is that it raises the material costs of manufacturing semiconductor devices. Typically, the carrier structure is used with plastic packages and is molded with the same molding compound used in the package body itself. With the carrier being almost four times the volume of the package body, material costs increase dramatically. In other applications, the carrier is made of another material, such as a metal or metal alloy, which also greatly increase material costs. The size of the leadframes is also increased and fewer devices can be made from one leadframe which further increases costs.
In addition to reducing lead damage, semiconductor manufacturers are also interested in reducing the number of handling operations to increase productivity. Once packages are excised from the leadframe, they are handled as individual units. For instance, a leadframe which is designed to make ten devices is handled as one unit until the devices are singulated, at which point the devices are considered ten units and require ten times the number of handling operations. Automated handling equipment is of considerable importance in increasing the manufacturer's productivity. But another way to increase productivity is to reduce the number of handling sequences required for the same number of devices. In other words, being able to keep the ten devices mentioned earlier as one unit would require one handling sequence at each operation, as opposed to ten. Thereby, productivity is increased.
Therefore, a need existed for an improved semiconductor device, more specifically for an improved device with a carrier structure, which would protect the leads of the package during various handling operations, testing, and shipment, which would reduce material costs over existing methods, and which would improve productivity.